Method and apparatus for the transportation of liquefied petroleum products



March 22, 1960 F. A. CLAUSON 2,929,221

METHOD AND APPARATUS FOR THE TRANSPORTATION OF LIQUEFIEID CTS Filed PETROLEUM PRODU Oct. 9, 1956 METHOD AND APPARATUS F OR THE TRANSPOR- TATIUN F LIQUEFIED PETROLEUM PROD- UCTS Frank A. Clauson, Roslyn Heights, N.Y., assignor to Texaco line, a corporation of Delaware Application October 1956, Serial No. 614,838

13 Claims. (CI. 62-54) This invention relates generally to low temperature insulation and in one specific embodiment is concerned with a method and apparatus for the transportation of liquefied petroleum gases.

Among the problems encountered in petroleum production is that of the release of large quantities of petroleum gases, which include the butanes, propane, ethane, and methane. Not only are these gases suitable for use in petro-chemical production and for fuel purposes, but also they are a valuable source with but slight processing for the enrichment of manufactured gas to be used for heating purposes. In domestic oil field production, utilization is accomplished by nearby facilities, while the transportation of petroleum gases from the fields to relatively distant points is largely by transcontinental pipelines.

The shipment of liquefied petroleum gases for considerable distances is feasible in containers which are built to withstand elevated pressures. However, the cost of manufacture of such containers due to the amount of material required, as well as the expense of transportation of the heavy containers, restricts the shipment to localized regions. At the same time, because of the maximum allowable metal wall thickness permitted without stress relief, the size of these containers is limited; for the larger size container would require a wall thickmess that would need stress relieving so that the size would be set by the size of the annealing furnaces.

. Other means for transporting liquefied petroleum gases at extremely low temperatures and at substantially atmospheric pressure which have been suggested but not proven successful in commercial operation include the use of insulated tanks mounted on barges or in vessels, the tanks being considerably larger than the pressurized containers and employing balsa wood for the eat insulation. Because of the amount of such insulation required, the usable dimensions andso the size of the tank container are reduced considerably. In addition, there is the danger of low temperature embrittlement of carbon steel tank walls which might occur should the insulation drop off. in the absence of the use of high cost alloy steels for constructing the tanks, the shipment of liquefied petroleum gases is restricted by safety standards to the relatively heavier petroleum gases, such as the butanes and propane, which have the higher boiling points.

Among therichest sources in the world of petroleum and petroleum gases are the Middle East oil fields of the Persian Gulf area. In this region, the amount of petroleum gas is fabulous and since it cannot be fully exploited either by further processing or by shipment through pipelines to areas where such can be accomplished, because of long distances or political unrest, it is allowed to be exhausted to the atmosphere or burned.

Over 70 percent of the petroleum and petroleum prod-- ucts exported from the Middle East oil fields are shipped peratures.

V 2,929,221 Patented 22 1960 gy deficiency can be reduced. Among the problems errcountered in shipping liquefied petroleum gases is that of the transportation and storage of these gases at their atmospheric boiling points and especially the insulation of the containers holding them at their low liquid tem- While it is known to transport and store liquefied gases, such as nitrogen and oxygen, in Dewar type containers consisting of spaced inner and outer receptacles, the problems involved in the construction of such type containers for the shipment of the amounts of liquefied petroleum gas required to justify their economical transportation prevents the use of the same.

Accordingly, it is an object of the present invention to provide a novel method of shipping liquefied petroleum gases.

It is another object of the invention to provide a new. and improved apparatus by which liquefied petroleum gases may be shipped economically over long distances.

Still another object of invention is to provide a novel method and apparatus for the shipment of low tempera ture materials in which the cost is negligible as com-. pared with other means.

Still another object of invention is to provide an economical method and apparatus for the shipment of liquefied petroleum gases in which the dangers of construction failure and of accumulation of explosive gas mix? tures are virtually eliminated.

These and other objects, advantages and features of the present invention will become apparent from the following description of the invention and by reference to the accompanying drawings wherein:

Fig. l is a partial diagrammatic view of a means for shipment of liquefied petroleum gases;

Fig. 2 is a vertical cross section taken through a cargo compartment of the means of Fig. 1, disclosing a spe-' cific embodiment;

Fig. 3a is a partial cross section of an alternate means for the insulation of a liquefied petroleum gas contain er; and

Fig. 3b is another partial cross section of another al ternate means for the insulation of a liquefied petroleum gas container.

in accordance with the illustrated embodiments of my invention, I employ the low thermal conductivity of wax to form an insulating layer around a low temperature container which is surrounded by a petroleum product. This has been found to be most applicable in shipment where the container for the low temperature product is separated from the outer vessel.

Referring to Fig. 1 of the drawing, there is disclosed in diagrammatic form, a partial view of an ocean-going tanker indicated at T, with a phantom partial section showing separate cargo tanks K, formed by the longitudinal and transverse bulkheads L and V respectively and the outer shell E of the tanker. One or more of the cargo tanks contains a liquefied petroleum gas container, which may be either circular or rectangular and is indicated at C, immersed in and surrounded by the cargo of crude or fuel oil 0, carried in the separate cargo tanks, K. These containers are supported in spaced relationship to the walls defining the separate cargo tanks by appropriate composite spacer elements, as at S formed of a steel member and a cap of wood or similar insulating material in contact with the container. The outlet for the container C is indicated generally at A and the access hatch for the oil cargo compartment is indicated at B, thecargo oil being discharged in the conventional manner through conduits leading to and from the pump house (all not shown).

Fig. 2 shows a cross section through a typical cargo tank illustrating the manner in which the applicant 'ac complishes his invention. This involves the build up of a 3 deposit from the cargo oil of a highly viscous material on the outer surface of the liquefied petroleum gas container C, this deposit including not only waxes contained in the cargo oil, but also other materials which cease to flow at low ambient temperatures and may include asphalt, grease and the like. In order to maintain this deposit in position against the wall of the inner container, it is proposed to use foraminous support means,

such as Wire cloth, spaced from the inner container at a predetermined distance and may include a number of such support means as required by the cargoes carried in the inner container and the outer cargo tank.

In the practice of the invention, it is proposed to cool the liquefied petroleum gas container at initial loading or after cleaning of the cargo tanks, by flash vaporization of the liquefied petroleum gas, compressing and condensing and recycling the evaporated gas in order to conserve the same, with the evaporation process reducing the temperature of the container C. As the container is cooled, a deposit begins to build up on the outer wall in contact with the cargo of crude or fuel oil. The thickness of this insulating deposit on the container C will build up automatically and adjust to the temperature of the liquified petroleum gas container, with the deposit renewing itself automatically, should it be removed by violent movement of the oil cargo around the tank during the voyage of the tanker. Optionally, if the characteristics of the liquefied petroleum gas and oil cargoes are such that a considerable thickness of the insulation layer is required prior to the start of the voyage, the hash vaporization process of the liquefied petroleum gas may be continued during its loading, with appropriate recycling recovery, until the temperature of the container C is reduced sufiiciently and the desired thickness of the insulating deposit layer is build up. In such an instance, it may be necessary to increase the wax content of the cargo oil so that a suitable thick insulating layer is deposited, and to aid in the depositing, some circulation of the cargo oil is helpt'ul. Alternatively, in order to expedite the loading of liquefied petroleum gases which require very low temperatures in their containers, it may be necessary to apply an initial layer of a'high melting point wax on the outer wall by mechanical means in order to provide an immediate insulating layer from the cargo oil. This may be done by spray application of a high melting point wax or by manual application of a wax paste mixture to result in a somewhat porous wax layer and so increase its insulating value.

In Fig. 2, the cargo oil is shown surrounding the liquefied petroleum gas container C, whichis spaced from the walls of the tank K by the elements S. The deposit support means is shown at D, retaining the deposit of viscous material M in position. Depending on the characteristics of the material of this deposit and the thickness of the layer to be formed, a plurality of support means D may be used, spaced apart at precalculated distances in order to retain the formed deposit in position.

"Figs. 3a and 3b disclose modifications of the insulating means by which the inner container C may be partially insulated prior to the start of the voyage for the transport of liquefied petroleum gases, the showing of the deposit support means being omitted for purposes of clarity. There is disclosed the wall W of the container C, upon which has been deposited a precalculated thickness of ahigh melting temperature wax X as an initial insulating layen. As .in the embodiment disclosed in Fig. 2, the start of the loading of the liquefied petroleum gases may require a flash vaporization process to reduce the inner temperature of the container C, after which the liquefied petroleum gas G maybe loaded without delay. This initial deposit of the wax X on the wall W is made to expedite shipment, and once the voyage is underway, the automatic deposit of an additional insulating layer at N may continue as the cargo oil in contact with the wax layer X is cooled, Thismanner of insulation is most helpful where the pour point of the cargo oil is so low that there must be a considerable flash evaporation at the start of the loading of the liquefied petroleum gas to deposition sufficient viscous material on the outer wall surface of container C to provide satisfactory insulation from the cargo of oil.

Fig. 3b shows a modification of the embodiment of Fig. 3a, disclosing a wall W of a container for liquefied petroleum gas G, to which is attached externally a precalculated thickness of a layer of balsa wood Y, upon which is deposited a predetermined thickness of high melting temperature wax X. As in the case of the structure disclosed in Fig. 311, an additional deposit of viscous material N forms on the'wax X as the ambient temperature of the cargo oil O is lowered. This manner of insulation is to be used with liquefied petroleum gases having the lower boiling points and/or where the cargo oils have lower pour points than those disclosed for use with the insulation of Figs. 2 and 3a. Alternatively, a layer of balsa wood or other insulating material can be attached to the inner wall surface for use with the modifications disclosed in Figs. 3a and 3b.

Thus, there has been disclosed a method and apparatus by which the cost of low temperature insulation is negligible as compared with other such insulation. In almost all the remote petroleum producing areas where low priced liquefied petroleum gases would be available, there would also be available crude oil or processed petroleum products for transportation to the consumer markets so that such a method and apparatus would be economically attractive.

Once the insulating deposit is formed, it is intended that it will be maintained during the return voyage. This will be accomplished by retaining part of the liquefied petroleum gas cargo G in the container C, so that during the process of evaporation of the liquefied gas, the container will remain at low temperature. Throughout the voyage, as the liquefied petroleum gas evaporates, it is compressed and recondensed and recycled or it may be used to provide for tanker fuel. When the tanker is laid up for overhaul, the deposit sloughs ofi or can be removed by warming so that both sides of the liquefied petroleum gas container may be inspected and repaired, if necessary.

The insulating layer formed and retained on the liquefied petroleum gas container, while increasing the dead weight of the tanker, is not particularly objectionable, since the liquefied petroleum gas carrier would have such a low bulk density that some ballast would be required. Since the greater proportion of this layer would be composed of wax, making it impermeable to and unafiected by water, the problem of frost spots caused by water freezing on normal external insulation to form high heat conductivity areas is eliminated. Thus the cargo space surrounding the liquefied petroleum gas containers C can be used for water ballast service as required on the return voyage.

Should there be a structural fault in the liquefied petroleum gas container C which allows leakage of the cargo oil inwardly, the external static pressure of the cargo oil surrounding the liquefied petroleum container exceeding that of the internal pressure in the container, the leaks would tend to be self-sealing by the formation of deposits of wax or the like.

In the event that there is a total structural failure of the liquefied petroleum gas container C, the liquefied petroleum gas will be vaporized by the cargo oil and cool the same, so that a viscous deposit would be formed on the shell of the tanker and so protect it from extremely low temperature, thus preventing its embrittlement and failure.

In addition, the complete cargo space of a tanker is utilized either by the liquefied petroleum gas containers or the cargo of oil resulting in minimum shipping costs. Also, there are no large void spaces subject to the accu mulation of hazardous explosive gas mixtures.

Although the foregoing description has been directed to the use of my invention for the transport of liquefied petroleum gas in an ocean-going tanker, it can be adapted quite readily to permanent shore installations for storage purposes and can be used in railroad tank cars for transport purposes. In the latter two instances, it is feasible to retain between the inner and outer receptacles, the product from which the insulating layer is deposited, which practice can be used also in tanker transportation.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method for maintaining a normally gaseous hydrocarbon in a liquid state in a container kept in spaced relationship with an outer receptacle open to atmospheric pressure including the provision of liquefied petroleum gas to said container, the provision to said outer receptacle of a petroleum product for surrounding said container and containing a constituent which is deposited as the ambient temperature of said product is decreased, and the formation of an insulating layer on the outer wall surface of said container, said insulating layer being maintained concomitantly by deposit of said constituent from said product during the time of residence of liquefied petroleum gas in its container.

2. The method of shipping liquefied petroleum gas which includes the providing of an inner container with liquefied petroleum gas, the providing of an outer container maintained in spaced relationship with said inner container and open to atmospheric pressure with a petroleum product having low heat conducting properties and containing material subject to deposit as the ambient temperature of said product is decreased, and the adding of an insulating layer to the outer wall surface of said inner container, said layer comprising material deposited from said product and being increased in thickness the longer said liquefied petroleum gas is retained in said inner container and being replenished concomitantly and automatically from said product.

3. The method of maintaining a normally gaseous hydrocarbon in a liquefied state for shipment and storage purposes including the steps of lowering the ambient temperature of an inner liquefied petroleum gas container held in spaced relationship with an outer container open to atmospheric pressure, providing a petroleum product having a relatively high content of material having a pour point above that of said ambient temperature of said inner container whereby a layer of said material is deposited on the outer surface of said inner container as said product fills said outer container, the deposit of said layer of said material being concomitant and automatic during the time said liquefied petroleum gas is retained in said inner container and said product in said outer container.

4. In the method as defined in claim 1, said insulating layer being applied initially by mechanical means so as to provide an immediate porous layer to increase the insulating value thereof and being increased in thickness by deposit of said constituent thereon.

5. An improved method for maintaining and for transporting a liquefied petroleum gas at substantially its boiling temperature and at atmospheric pressure comprising the steps of surrounding a container for said liquefied petroleum gas by a wax-containing hydrocarbon fluid at atmospheric pressure, lowering the temperature of said container so that petroleum gas may be maintained substantially in its liquid state therein, providing said container with said liquefied petroleum gas and maintaining the temperature and pressure conditions therein so that the ambient temperature surrounding said container for said liquefied petroleum gas is lowered to the point that the wax contained in said hydrocarbon fluid is deposited on the outer wall surface of said container.

6. An apparatus for maintaining a petroleum gas in liquefied form comprising the combination of an inner receptacle and an outer receptacle and means for supporting'and maintaining said inner receptacle in spaced relationship with said outer receptacle, said outer receptacle being open to the atmosphere and containing a petroleum product having low heat transmission properties and containing material having low thermal conductivity which is deposited therefrom as the ambient temperature thereof is decreased, said inner receptacle being adapted to receive liquefied petroleum gas whereby the ambient temperature thereof on the outer wall surface of said inner container is lowered to cause a deposit of said material from said fluid to form thereon, concomitantly with the presence of said liquefied petroleum gas in said inner receptacle. 1

7. An apparatus as defined in claim 6, wherein said product surrounding and in contact with the outer wall surface of said inner receptacle has tendencies to form a deposit of wax and other viscous material thereon as the ambient temperature surrounding said inner receptacle is lowered.

8. An apparatus as defined in claim 7, wherein said inner receptacle has foraminous support means spaced from the outer wall surface thereof for retaining material deposited from said product.

9. In an apparatus as defined in claim 7, said product being enriched as required with material desired to be deposited.

10; In a combination of spaced inner and outer receptacles wherein liquefied petroleum gases are shipped 11. In the combination as defined in claim 10, said' inner layer having high melting temperature characteristics being spaced from said outer wall surface of said inner receptacle by a predetermined thickness of an insulating material having low heat conducting properties such as balsa wood.

12. In the combination as defined in claim 10, said inner receptacle having a layer of insulating material attached to the inner wall surface thereof.

13. In the combination as defined in claim 1, said inner receptacle having a layer of insulating material attached to the inner wall surface thereof.

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